The present invention relates to a fuel cell system and to fuel cell system control method.
Conventionally, there has been known a fuel cell system in which hydrogen stored in a high-pressure hydrogen tank is supplied to a fuel cell via an injector and moreover in which an anode exhaust gas containing hydrogen that, although once supplied to a fuel cell, has not been used for power generation is circulated by a circulation pump so as to be supplied once again to the fuel cell (JP 2008-235020 A).
It has been desired heretofore that fuel cell systems be improved in power generation efficiency. As one of causes that lead to degradation of the power generation efficiency of fuel cells, there is a case in which hydrogen supplied to the anode permeates through an electrolyte membrane without being used for power generation reaction so as to leak to the cathode side (hereinafter, also referred to simply as ‘cross-leak’), with the result that hydrogen is not utilized for power generation but consumed. Particularly in intermittent operations, most of hydrogen supplied from the injector is consumed for the cross-leak, resulting in degraded power generation efficiency. The term, intermittent operation, in this case include to a state of a vehicle with a fuel cell system mounted thereon in which state the power generation of fuel cells is temporarily halted during a low-load operation while electric power is supplied from a secondary battery to a load (vehicle motor or the like), and to a state in which small power generation is executed at an extremely low load during a process of high-potential avoidance control or the like. The low-load operation is exemplified by such a state as an idling state, a low-speed running state or a regenerative braking state. The term, high-potential avoidance, refers to such control that an output voltage of the fuel cell is made to be a high-potential avoidance voltage smaller than an open circuit voltage (OCV) in order to suppress progression of deformation of a catalyst metal contained in the anode or the cathode in above-mentioned intermittent operations.